ABSTRACT: Repeated interaction and social networks are commonly considered viable solutions to collective action problems. This article identifies and systematically measures four general mechanisms— that is, generalized altruism, group solidarity, reciprocity, and the threat of sanctioning— and tests which of them brings about cooperation in the context of Ugandan producer organizations. Using an innovative methodological framework that combines “ lab-in-the-fi eld” experiments with survey interviews and complete social networks data, the article goes beyond the assessment of a relationship between social networks and collective outcomes to study the mechanisms that favor cooperative behavior. The article first establishes a positive relationship between position in the network structure and propensity to cooperate in the producer organization and then uses farmers’ behavior in dictator and public goods games to test different mechanisms that may account for such a relationship. Results show that cooperation is induced by patterns of reciprocity that emerge through repeated interaction rather than other-regarding preferences like altruism or group solidarity.